Pressure-relief valve with teflon seal

ABSTRACT

A pressure-relief valve for the protection of hydraulic units in underground mining, functionable against a sudden overload in pressure, is provided including a valve housing having an upper part and a connection piece, a valve spring lodged against the upper part, a valve piston longitudinally slidable within the connection piece and engageable forceably at one end against the valve spring and having a blind bore and radial bores communicating perpendicular thereto through which a pressure medium is flowable, and at least one sealing ring against which the piston travels which is arranged in the connection piece. The sealing ring is positioned to adjoin the radial bores, consists of a very hard plastic material producing very low friction and has a rectangular cross section.

FIELD OF THE INVENTION

The invention relates to a pressure-relief valve for the protection ofhydraulic units in underground mining, particularly of hydraulic facesupport systems, against sudden overload due to rock pressure or similarcauses, with a valve piston in the valve housing, slidable in the inletbore against the force of a valve spring and closing off the pressuremedium with respect to the outlet bores, this piston having a blind boreand therefrom starting radial bores, which are shaped to correspond witha sealing ring provided in the connection piece.

THE RELATED ART

Such pressure-relief valves, also known as safety valves, are used therewhere systems, particularly hydraulic struts systems in undergroundmining are in danger of being damaged by excessive pressures. Thesehydraulic struts are arranged either as individual struts or as anintegrated shield-type support. Because of the particular dangersinvolved, there are official requirements for providing pressure-reliefvalves for such shield-type support systems, but also for individualhydraulic struts, in order to prevent permanent damage or evendestruction endangering the miners in cases of overload From DE-OS 28 30891 a pressure-relief valve is known, wherein excessive pressure in thehydraulic system is reduced by means of a valve spring stressed betweenthe locking screw and the valve piston On the valve spring cap or thevalve spring retainer a conically or spherically shaped valve-closingbody is provided which is lifted off the valve seat in case of overload.On the piston a damping cylinder is provided, which limits the flowpassage opening. However, such valves do not afford the locking safetyrequired for the use as pressure-relief valves or safety valves inmining. Furthermore, an accurate positioning, particularly of the springis very difficult, which means that another requirement, the one for asafe response of such mining safety valves is not fulfilled.

From the DE-OS 33 14 837 another pressure-relief valve is known whereinthe valve spring is arranged in the valve housing so that it presses onthe valve spring cap and thereby on the valve piston and this wayinfluences the opening of the valve corresponding to the setting. Thevalve piston is slidably guided on a piston-pin bore formed in theguide, whereby the required sealing is provided by an O-shaped annularseal located in a groove. Each time, the O-ring has to be completelyoverriden by the radial bores of the valve piston, before the pressuremedium can exit in case of overload. Due to this excessive load, suchO-ring valves have a short operational life. A further drawback of theseknown pressure-relief valves are the low flow rates of only 40 to 100liter per minute. This is not satisfactory for the required safety andquick response of such valves. Besides, it is disadvantageous that thevalve springs involved have to use wire of considerable thickness andhave considerable coil diameters in order to counteract the pressure,which again requires corresponding overall valve dimensions. The higherthe flow rate, the bigger must be the valve springs, and thereby theentire valve housing. Particularly in underground mining it is alreadynot possible to use such valves, only because of their large dimensions.Also, the required cross sections for the evacuation of pressure mediumare not available. Attempts have been made to increase the flow rate byusing larger valve pistons and by conferring a special configuration tothose valve pistons, as well as by assigning a control piston. However,the response time remains unsatisfactory in this case because theO-rings produce too much friction. As a result of such unsatisfactoryclosing values, the operation of the valves is too inaccurate.Furthermore, the operational life of such O-rings is very unfavorable.

It is the object of the present invention to create a pressure-reliefvalve with favorable closing values and with seals insuring effectiveand long-term operation.

DETAILED DISCUSSION

The problem is solved according to the invention in that the sealingring assigned to the valve piston is made of a very hard plasticmaterial producing minimal friction.

Surprisingly favorable closing values are achieved this way, because thefriction is reduced so much that even the movements of a valve pistonwith a very large diameter are not impaired by friction. Such sealingrings, which are no longer flexible, still afford an efficient seal,have a very long life and make possible the already-mentioned favorableclosing values, because the friction between the sealing ring and valvepiston is reduced to a minimum. A controlled sealing is reached becausethe sealing ring is formed exactly on the sealing edge of an annularsealing zone. The sealing ring has a hardness of 50-90 shore D,preferably of 54-60.

Advantageous sealing combined with friction which is still low can beachieved when the sealing rings have a rectangular cross section. Suchsealing rings lead to a level seal, and the occurring friction can notnoticeably impair the movements of the valve piston. This way it is alsoadvantageously possible to shape the sealing piston for instance like atubular sleeve with a very large diameter, which leads to a considerableincrease in the admissible and possible flow rate, particularly when acontrol piston having a smaller diameter is used on the valve piston.The rectangular configuration of the sealing ring facilitates assemblyand insures a safe lodging in the assigned groove.

A particularly advantageous embodiment of the invention proposes thatthe annular groove receiving the rectangular sealing ring be provided atthe sealing edge with a bevel in the groove bottom. Due to this, thesealing ring forms precisely in the area of the sealing edge the desiredannular sealing zone, as a result of the fact that when it is introducedin the annular groove, in this area it is strained to such extent thatit will press itself against the sealing piston and will provide here apermanent annular seal. As proposed by the invention, in order to keepthe dimensions of the sealing ring within limits and still be able toinsure an effective seal, the bevel connects the groove bottom and thesupport wall which runs slightly above the radial bores of the closedvalve. This bevel takes care of the described deformation of the sealingring and presses it close against the moving sealing piston, wherebyespecially the material of the sealing ring insures that the desired andpredetermined sealing zone is observed also during longer operationinterruptions, i.e. when the pressure-relief valve is not triggered.

A controlled fit of the sealing ring in the area of the sealing edge isreached when the bevel is arc-shaped. Besides, this configurationprotects the sealing ring from damage while it fits the sealing pistonsnugly, an already mentioned advantage. In a pressure-relief valve witha throughflow rate of more than 2000 liter, it is still possible to workwith favorable overall dimensions when in a valve piston with integratedcontrol piston and between the transverse bores forming chambers withequal pressure and serving as outlet bores, sealing rings are providedon both sides of the transverse bores, whereby the bevels are formed onthe opposite support walls. Although there are now two, even threesealing rings hampering by friction the movements of the valve pistonand the control piston, particularly their return stroke, a quick returnstroke of the piston is insured, because of the special design of thesealing rings, which afford a complete sealing and at the same time donot at all or only insignificantly hamper the valve piston and controlpiston. It is also advantageous that thereby wider sealing rings can beused, without increasing the friction significantly. Thereby, it isadvantageous to make also the sealing ring assigned to the controlpiston of a plastic material producing little friction and to arrange itin a groove with a bevel.

In a particularly advantageous embodiment facilitating the production,the sealing ring is cut off by turning from a plastic tube. This way,the suitable configuration can be preserved, without creating additionalmanufacturing expenses. Such sealing rings can be produced in largequantities and very quickly, without great expense.

Particularly advantageous has proven a plastic teflon

A sealing ring made of this plastic teflon material TFM 1600®. A sealingring made of this plastic teflon material TFM 1600® has low flexibility,but handles perfectly, namely even then when in the annular groovesbevels are provided, as proposed by the invention. Based on the level,respectively controlled sealing achieved by the rectangularly shapedsealing rings, this material is advantageous because of its specialcomposition, particularly with regard to the low friction. Furthermore,there can be insured with this plastic teflon material TFM 1600® a verylong service life of the pressure-relief valves.

Since, as already mentioned the teflon® sealing rings have littleflexibility, special measures have to be taken in order to place themefficiently in the area of the sealing piston. According to theinvention, this is achieved by inserting in the inlet bore of theconnection piece, on the inlet side, an inwardly and outwardly steppedplug-in socket equipped with an O-ring, affixing the sealing ring. Onthe other hand, in order to affix the upper sealing ring, if available,a guide screw with an O-ring is provided in the connection piece in theinlet bore on the outlet side, which fastens the upper sealing ring andat the same time guides the control piston. This way, on the inlet side,and if necessary on the outlet side too, an efficient fastening of therespective sealing ring is achieved in correspondence with the openingdirection of such a pressure-relief valve. The plug-in socket isadvantageously actuated by the pressure of the pressure medium and fixedin the connection piece, without being locked or screwed in. On theother hand, the guide screw is screwed in from the spring space andthereby efficiently locks the upper sealing ring, preventing anymovement of the same from its position in the assigned annular groove,while in operation

The invention is remarkable especially due to the fact that it improvesconsiderably the modus operandi of the pressure-relief valve, insuringexceptionally favorable closing values and service life, because thevalve piston is not impaired or hindered by the friction of the sealingrings, and as a result these rings are gently treated. With the solutionproposed by the invention, first of all it is possible to selectpractically any diameter for the sealing piston, since their movement,especially during the return stroke, are hindered so little by theforcibly required sealing rings that the movement of the valve piston ispractically not influenced, even when it has a considerably enlargeddiameter. Due to the very large diameter of the valve piston, suchpressure-relief valves can allow for a flow rate of up to 2000 liter andmore, thus advantageously meeting the requirements of undergroundmining.

BRIEF DESCRIPTION OF THE DRAWING

Further details, advantages and objects of this invention may be seenfrom the following description of the pertaining drawing, showing apreferred embodiment with the thereto related details. The drawingshows:

FIG. 1 a simple pressure-relief valve with rectangularly shaped teflonsealing rings,

FIG. 2 an enlarged representation of the valve according to FIG. 1 inthe sealing area,

FIG. 3 a schematic representation of the pressure-relief valve accordingto FIGS. 1 and 2, detailing in an enlarged reproduction the bevels inthe annular grooves,

FIG. 4 a pressure-relief valve with differential valve piston in sectionand,

FIG. 5 an enlarged reproduction of the sealing area of thepressure-relief valve shown in FIG. 4.

DETAILED DESCRIPTION

FIG. 1 shows a pressure-relief valve (1) with a basically two-part valvehousing (2), whereby the upper part (3) and the connection piece (4) arescrewed together. The connection piece (4) is here connected via aplug-in connection, for instance with a hose or a with a unit to beprotected, while according to FIG. 4 an outer connection thread (9) isprovided, by means of which such a pressure-relief valve (1) can bescrewed to the unit to be protected.

Inside the valve housing (2), the valve piston (10) is supportedslidably against the force of spring (11) in the inlet bore (13). Thevalve spring (11) does not fill up the spring space (12). It restsagainst the inner wall of the upper part (3) and allows the passage ofthe pressure medium from inlet bore (13) via the blind bores (14) andthe radial bores (15, 16), whereby the respective opening value of thepressure-relief valve (1) can be preselected by an adjusting screw (21).In the adjusting screw (21) a bore is provided for the discharge of thepressure medium.

When the valve is triggered, the valve piston (10) has to travel overthe sealing ring (19) lodged in an annular groove (55). The specialconfiguration of the annular groove (55) is clearly shown in FIGS. 2 and3.

The valve piston (10) rests against the spring plate (26) bearing thevalve spring (11), which on the opposite side rests against the setscrew (21), respectively on the upper part (3).

The outer wall (29) of the valve piston (10) is smooth, so that it canmove without difficulty along the sealing ring (19), as shown in FIG. 2.Thereby, a close fit of the sealing ring (19) together with an optimalsealing is achieved above the radial bores (15, 16) precisely in thearea of the sealing edge (56) due to the fact that the groove bottom(57) and the support wall (59) are connected over a bevel (58), as shownin FIGS. 2 and 3. This leads to the deformation, respectively theforcible deformation of the sealing ring (19), so that an even closerfit is insured in the area of the sealing edge (56). Thereby, the bevel(58) is advantageously curved or arc-shaped, in order to prevent thedamaging of sealing ring (19) made of a very unyielding material.

By comparison, FIG. 3 details the arrangement of a sealing ring (19)lodged in a regular groove (right side) and of a sealing ring lodged ina groove with a bevel (58) (left side). In order to fasten the sealingring (19) the bore in the connection piece (4) is enlarged so that thefastening pipe segment (65) can be inserted to hold the sealing ring(19) in position. With the aid of arrows it is shown where the sealingring (19) is particularly closely fitted to the valve piston (10).

In the embodiment of FIGS. 4 and 5, a tubular sleeve (20) with a largeflow-discharge surface is provided as valve piston (10). This tubularsleeve (20) has a blind bore (14) and radial bores (15, 16). Here too,care is taken to avoid the penetration of the pressure medium from thearea of the inlet bore (13) into the pressure-relief valve (1), by meansof the special sealing ring (19). The outer wall (29) of the sealingpiston (10), respectively the tubular shell (20) is completely smooth,so that when it rides over the sealing ring (19) only normal friction isproduced. On the sealing piston (10), centrally and thereby in the valveaxis, a control piston (60) is formed, which is loaded via valve spring(11) in a direction opposite to the opening direction (61). This valvespring (11) is here also supported on the valve set screw (21),respectively the valve plate (26) which rests against the control piston(60). The valve spring (11) arranged in the valve space (12) can therebyefficiently act upon the control piston (60) and thereby also on thevalve piston (10), so that they can open only when the set spring forceis surpassed. The setting of the valve spring (11) takes place over thealready mentioned adjusting screw (21), which is twistably arranged onthe head part. It has a hexagonal socket, in order to simplify theadjustment.

The sealing of the valve piston (10) designed as a tubular sleeve (20)takes places on the one hand, as already mentioned, over the lowersealing ring (19) lodged in an annular groove (55) and on the otherhand, over the sealing ring (51) lodged in the annular groove (50).

The pressure medium streaming through the inlet bore (13) into thepressure-relief valve (1) flows via blind bore (14) until it reaches thelid (79) representing the upper limit of the valve piston (10). This lid(79) is provided with flow passages (80, 81), so that the pressuremedium present in the blind bore (14) flows at the same time also intothe area above the valve piston (10), so that the latter maintains itsillustrated position, because the pressure conditions are the same inboth chambers (46, 47). At the same time, the pressure-medium flowpasses through the control piston (60), which has a blind bore (62) andon its extremity, radial bores (63, 64). The control piston (60) withits blind bore (62) and its radial bores (63, 64) is sealed off withrespect to the spring space (12) by the sealing ring (75) which also hasa groove (76) with bevel (77), so that only when this sealing ring (75)is overriden, can the pressure medium penetrate the spring space (12).Due to the design of the valve piston (10) and the flow-passage openings(80, 81) provided in the lid (79), this becomes possible only when theforce of the valve spring (11) is surpassed, for instance when thehydraulic unit is subjected to a correspondingly excessive load as aresult of rock pressure. Since the outer wall of the control piston (6)is smooth and this sealing ring (75) has a relatively reduced diameter,the occurring friction forces are so low that the closing values of thevalve as a whole are not impaired.

The sealing rings (19, 51) rub against the outer wall (29) of the valvepiston (10), respectively the tubular sleeve (20), thereby protectingthe area of the transversal bore (17) and therewith the surroundingsfrom the exit of the pressure medium. When the valve piston (10) isdisplaced or moved, this friction leads intentionally to an impairmentof the travel motion. When the valve is triggered, this remainsnegligible, but during the return stroke it insures favorable closingvalues when these sealing rings (19, 51) are made of a plastic teflonmaterial TFM 1600®. Such sealing rings with rectangular cross sectionsresult in clearly favorable sealing values, but produce very littlefriction, so that the travel of the valve piston (10) are hindered to aconceivably small extent. Due to the hardness of this plastic teflonmaterial, optimal service life is achieved and as a result of the use ofrectangular sealing rings an improvement of the overall sealing isreached particularly in cooperation with the bevels (58, 54 and 77).Namely the sealing ring (51) also rests in an annular groove (52) with abevel (54) connecting the support wall (52) and the groove bottom (53).

The lower sealing ring (19) lodged in the annular groove (55) can beeasily mounted, in spite of its reduced flexibility, since in the inletbore (13) a plug-in socket is introduced from the opening direction(61). This plug-in socket (85) is sealed downwardly by the sealing ring(86) and the support ring (87) and upwardly by the O-ring (88) and thesupport ring (89). This is shown clearly especially in FIG. 5. The upperarea or also the inner area of the pressure-relief valve is safeguardedand sealed by the sealing ring (51) as per FIGS. 4 and 5, since it isfastened via the guide screw (90) which is sealed via O-ring (91) andsupport ring (92). The mounting of the screw guide (90) is facilitatedby the recesses (93), which make possible a direct screwing into thethread. Besides, the plug-in socket (85) can be easily inserted, sinceby design it is under the action of the pressure medium and is pressedinto the connection piece (5). The opening of the inlet bore (13) iscorrespondingly widened, in order to receive the plug-in socket (85) aswell as the guide screw (90).

I claim:
 1. A pressure-relief valve for protection of hydraulic units inunderground mining functionable against a sudden overload in pressure,comprising:a valve housing including an upper part and a connectionpiece; a valve spring lodged in said upper part; a valve piston arrangedand longitudinally slidable within said connection piece, said valvepiston being engageable forceably against said valve spring, said valvepiston including a blind bore and radial bores, said radial bores beingperpendicular to and communicating with said blind bore, and a pressuremedium being flowable through said bores; at least one sealing ringarranged in said connection piece over which said piston travels, saidsealing ring being positioned to correspond adjoiningly with said radialbores, and said sealing ring consisting of a very hard plastic materialproducing very low friction and having a rectangular cross section; andat least one annular groove within said connection piece receiving arespective said rectangular sealing ring, said at least one annulargroove being defined by a groove bottom and a support wall perpendicularthereto with a bevel connecting said groove bottom and said supportwall.
 2. The pressure-relief valve according to claim 1, wherein saidsupport wall is arranged slightly above said radial bores when saidrelief valve is in a closed position.
 3. The pressure-relief valveaccording to claim 1, wherein said bevel is arc-shaped.
 4. Thepressure-relief valve according to claim 1, wherein said valve piston isan integrated control piston formed with a chamber, said connectionpiece further including transverse bores therewithin serving as outletbores from said chamber upon communication of said radial borestherewith, one of said sealing rings being provided above and anotherbelow said transverse bores in respective annular groove formed in saidconnection piece, each of said grooves having a respective bevel at arespective support wall.
 5. The pressure-relief valve according to claim1, wherein a further one of said sealing rings is lodged in a furthergroove with a respective bevel, said further sealing ring beingpositioned above the sealing rings provided above and below saidtransverse bores and formed of a plastic material producing littlefriction.
 6. The pressure-relief valve according to claim 4, furthercomprising an inlet bore leading into said connecting piece at an endthereof opposite an end of said connecting piece contacting said valvespring, and an inwardly and outwardly stepped plug-in socket beinginserted within said inlet bore, said plug-in socket including an O-ringand being fastened against a lowermost one of said sealing rings.
 7. Thepressure-relief valve according to claim 4, further comprising an inletbore within said connecting piece, and a guide screw arranged on anoutlet side of said inlet bore, said guide screw having an O-ring andfastening one of said sealing rings that is closest to said valve springwhile at the same time guiding said control piston.
 8. Thepressure-relief valve according to claim 1, wherein the plastic materialforming the at least one sealing ring is formed of apolyperfluoro-olefin.